1. Field of the Invention
The present invention relates to a vacuum pump, for instance a turbo-molecular pump, that evacuates a vacuum vessel.
2. Description of the Related Art
In vacuum pumps such as turbo-molecular pumps or the like, there is a very small clearance between a stator portion and a rotor portion in which rotating blades or the like rotate at high speed. As a result, contact between the rotor portion and the stator portion occurs in case that, for instance, solid products such as aggregates in the evacuated gas become deposited on the vacuum pump, or when a rotary body deforms due to creep, or in case of advanced wear of protective bearings.
Serious problems can ensue if such state of contact between the rotor portion and the stator portion is not addressed through maintenance (overhaul).
Maintenance periods have been conventionally anticipated in accordance with techniques set forth in, for instance, Japanese Patent Application Laid-open Nos. H6-330885, H6-101655 and 2004-117091. Reaching a stage by which the vacuum pump is no longer re-useable has been averted conventionally through prompting the execution of maintenance at appropriate periods.
Japanese Patent Application Laid-open No. H6-330885 proposes the features of detecting the runout amount of a rotor using a position sensor, and issuing an alarm and stopping a pump, when the detected runout amount exceeds a reference runout amount.
Japanese Patent Application Laid-open No. H6-101655 discloses the feature of directly measuring the amount of deposited solid product (foreign matter) using a capacitive-type membrane pressure sensor.
Japanese Patent Application Laid-open No. 2004-117091 discloses the feature of measuring a temperature difference between the temperature of a gas flow path and the temperature of a portion that is not a gas flow path, and measuring the amount of solid product deposited in the gas flow path on the basis of the temperature difference.
In the technique set forth in Japanese Patent Application Laid-open No. H6-330885, however, it was not possible to discriminate between an increase in vibration amplitude caused by growing unbalance of a rotary body over time, and an increase in vibration amplitude caused by physical contact between a rotor portion and a stator portion.
Also, it was not possible to distinguish between an increase in vibration amplitude caused by mechanical vibration in response to, for instance, opening and closing of a vacuum valve to which a pump is connected, or caused by external vibration applied to a device (vacuum vessel or the like) to which the pump is connected, and an increase in vibration amplitude caused by physical contact between a rotor portion and a stator portion.
Thus, it is a first object of the present invention to provide a vacuum pump where physical contact between a rotor portion and a stator portion can be detected with good precision.